I still feel attached but she doesnt care?

Still feel attached to my ex gf. Togtehr for three years and broke up 3 . She's talking to a new guy already, for me it's too early I can't even think of other girls, as I'm still in love with my ex. I think about her constantly and panic wh n I think of them together. I'm sick of feeling like this but nithing can stop it. I've tried so hard to stop but I can't. She was talking to me up until this new guy appeared then she disappeared. Completely gone. Then out of the blue a couple of days ago she tagged me in a advert on Facebook? I commented on it and she never acknowledged? She doesn't even care about me and I'm still love her. What can I do? I understand why she still tagging me, she must of thought about me but she is talking to a new guy. I dated a new girl but I wasn't but attracted to her. My attraction towards other girls seems to have switched off